WordPress: Get post id by meta key and value

get_post_id_by_meta_key_and_value.php

<?php
if (!function_exists('get_post_id_by_meta_key_and_value')) {
	/**
	 * Get post id from meta key and value
	 * @param string $key
	 * @param mixed $value
	 * @return int|bool
	 * @author David M&aring;rtensson <david.martensson@gmail.com>
	 */
	function get_post_id_by_meta_key_and_value($key, $value) {
		global $wpdb;
		$meta = $wpdb->get_results("SELECT * FROM `".$wpdb->postmeta."` WHERE meta_key='".$wpdb->escape($key)."' AND meta_value='".$wpdb->escape($value)."'");
		if (is_array($meta) && !empty($meta) && isset($meta[0])) {
			$meta = $meta[0];
		}		
		if (is_object($meta)) {
			return $meta->post_id;
		}
		else {
			return false;
		}
	}
}